There is substantial literature in the art with respect to the hydrogenation of aromatic amines, including bridged aromatic amines, e.g., methylenedianiline to produce 4,4'-methylenedi(cyclohexylamine), also called bis(para-aminocyclohexyl)methane, bis(4-aminocyclohexyl)methane and PACM.
The hydrogenated form of these aromatic amines, typically exists as a mixture of isomers, e.g., the cis,cis- (c,c); cis,trans- (c,t); and trans,trans- (t,t). Often it is desirable to produce a product having a specific isomer content as the isomer content in the mixture not only influences the physical form of the mixture but also influences the properties of products in which they are incorporated. In the case of PACM, a low trans,trans- isomer content (20%) in the mixture, commonly referred to as PACM-20, exists as a liquid product while a mixture high in trans,trans- isomer content (48%), commonly referred to as PACM-48, leads to a solid form. For certain applications, such as the manufacture of polyamide fibers and epoxy additives, it often is beneficial to use PACM-48 instead of PACM-20.
Commercially, PACM-48 is produced through continuous processing conditions, where catalyst loading and reactor residence times are sufficient to yield the product of thermodynamic control. Batch processing conditions produce PACM-48 from MDA inefficiently due to excessive reaction times required for complete isomerization to the product of thermodynamic control.
Some of the early hydrogenation work to produce aromatic amines, such as, PACM, was done by Whitman and Barkdoll, et al. and their work is set forth in a series of U.S. Patents, e.g., U.S. Pat. Nos. 2,511,028; 2,606,924; 2,606,925; and 2,606,928. Basically the processes described in these patents involve the hydrogenation of methylenedianiline at pressures in excess of 200 psig, preferably in excess of 1,000 psig, at temperatures organic solvent is used in the hydrogenation process. Typically, a liquid product having a trans,trans- content of 15-23% is obtained. Examples of ruthenium catalysts utilized for the hydrogenation process include ruthenium oxides such as ruthenium sesquioxide and ruthenium dioxide; and ruthenium salts.
U.S. Pat. Nos. 3,347,917; 3,711,550; 3,679,746; 3,155,724; 3,766,272 and British Patent 1,122,609 disclose various isomerization processes and hydrogenation processes to produce PACM containing high trans,trans- isomer content; i.e. an isomer content near equilibrium typically 50% trans,trans, 43% cis,trans- and 7% cis,cis-. As in the early work ruthenium catalysts usually were used to effect isomerization. Higher temperatures and longer reaction times were required to produce the high trans,trans- product and, in addition, considerable deamination of product took place.
A wide variety of catalytic systems have been developed for the hydrogenation and isomerization of aromatic amine, and typical catalytic systems are represented in the following patents:
U.S. Pat. No. 3,591,635 discloses the use of rhodium on alumina as a catalyst for the hydrogenation of methylenedianiline.
U.S. Pat. No. 4,946,998 discloses processes for the hydrogenation of methylenedianiline contaminated with impurities utilizing a mixture of rhodium and ruthenium as the catalyst. A hydrogenated methylene-dianiline product having a trans,trans- isomer content of from about 14 to 28% is prepared using the mixed metal catalyst system, although higher trans,trans- content can be achieved through high temperature, long reaction times, and high ruthenium concentration. The presence of rhodium permits lower operating temperatures and reduces the percent trans,trans- isomer.
U.S. Pat. No. 3,520,928 discloses the low pressure hydrogenation of mineral acid salts of aromatic primary amines and aqueous solution using a platinum or palladium catalyst.
U.S. Pat. No. 3,558,703 and U.S. Pat. No. 3,634,512 disclose the catalytic hydrogenation of diaminodiphenyl alkanes and ethers utilizing a cobalt or nickel catalyst promoted with manganese and base modified derivatives thereof ('512). The '703 patent discloses that other conventional catalysts may be incorporated into the catalyst component of cobalt or nickel, and such metals include copper, chromium, nickel, tungsten, molybdenum, platinum, palladium and ruthenium in amounts up to about 10% by weight.
U.S. Pat. No. 3,445,516 discloses the hydrogenation of toluenediamine utilizing a variety of catalysts including Raney nickel, Raney cobalt, cobalt oxide and mixtures of cobalt oxide and alkaline earth metal oxide, such as calcium oxide in combination with sodium carbonate.
U.S. Pat. Nos. 3,679,746 and 4,020,104 disclose the isomerization of a PACM and PACM-type product low in trans,trans-isomer content to one of high trans,trans- isomer content using ammonia and a ruthenium catalyst.